Device and method for measuring an electric current

ABSTRACT

A current measuring device for measuring the current through one or a plurality of conductors (L 1,  L 2,  L 3 ) of an array of n conductors, n being a natural number≧2, comprises n+1 magnetic-field-sensitive sensors (S 1  to S 4 ) which are arranged such that two respective magnetic-field-sensitive sensors are arranged adjacent a respective conductor. A unit ( 12 ) for reading out output signals of the magnetic-field-sensitive sensors is provided. Furthermore, the current measuring device is provided with a unit ( 10 ) for calculating the current through one or a plurality of conductors on the basis of the read output signals and on the basis of coefficients which describe the influence of currents flowing through each of the n conductors and of a constant magnetic field on the output signal of each of the magnetic-field-sensitive sensors.

The present invention relates to a device and a method for measuring anelectric current and, in particular, to a device and a method formeasuring the electric current flowing through one or a plurality ofconductors of an array of several electric conductors which are arrangedin close proximity to one another.

For potential-free current measurement it. is known to place twomagnetic-field-sensitive sensors on both sides of an electric conductor.Such an arrangement is schematically shown in FIG. 1, where twomagnetic-field-sensitive sensors 2 and 4 are arranged on both sides ofan electric conductor 6. By means of the magnetic-field-sensitivesensors 2 and 4, the magnetic field generated by a current flowingthrough the conductor 6 is measured. The current in the conductor isdetermined by forming the difference between the output signals of thetwo magnetic-field-sensitive sensors 2 and 4; this principle permits anexisting, gradient-free magnetic field to be eliminated when the currentis being measured. The above-described arrangement is disadvantageousinsofar as 2n sensors are required, when the currents in n conductorsare to be measured simultaneously. The known method is also problematicwhen the currents through a plurality of conductors are to be measuredand when the conductors are arranged in closely spaced relationship withone another. This will give rise to a magnetic field gradient at thelocation of a conductor due to the current of a neighbouring conductorso that the current measurement will be disturbed. The influence of themagnetic field gradient caused by the current in the neighbouringconductor cannot be compensated for.

It is the object of the present invention to provide a device and amethod for measuring the current through one or a plurality ofconductors of an array of n conductors making use of a reduced number ofmagnetic-field-sensitive sensors, which additionally permit an exactdetection of the current through one of the conductors even if theindividual conductors of the conductor array are arranged in closeproximity to one another.

This object is achieved by a current measuring device according to claim1 and a method according to claim 8.

The present invention provides a current measuring device for measuringthe current through one or a plurality of conductors of an array of nconductors, n being a natural number≧2, in the case of which n+1magnetic-field-sensitive sensors are arranged in such a way that tworespective magnetic-field-sensitive sensors are arranged adjacent arespective conductor. Furthermore, a unit for reading out output signalsof the magnetic-field-sensitive sensors is provided. Finally, thecurrent measuring device is provided with a unit for calculating thecurrent through one or a plurality of conductors on the basis of theread output signals and on the basis of coefficients which describe theinfluence of currents flowing through each of the n conductors and of aconstant magnetic field on the output signal of each of themagnetic-field-sensitive sensors.

The present invention thus permits a reduction of the requiredmagnetic-field-sensitive sensors from 2n to n+1, when the currentflowing through n conductors is to be detected. In addition, the presentinvention permits a compensation of influences, which are caused byclosely spaced, current-carrying conductors, on the current measurementin one conductor. It follows that the present invention provides, on theone hand, a relatively simple current measuring device, which provides,on the other hand, exact results in the case of electric conductorsarranged in close proximity to one another.

The magnetic-field-sensitive sensors are preferably Hall sensors whichare monolithically produced on a semiconductor substrate together withthe evaluation electronics, i.e. the read-out unit and the calculatingunit, and, preferably, together with a memory for storing thecoefficients.

The present invention additionally provides a method of measuring thecurrent through one or a plurality of conductors of an array of nconductors, n being a natural number≧2, wherein the output signals ofn+1 magnetic-field-sensitive sensors are first read out, two respectiveones of these sensors being arranged adjacent a respective conductor.Subsequently, the current through one or a plurality of the conductorsis calculated on the basis of the read output signals and on the basisof coefficients which describe the influence of currents flowing througheach of the n conductors and of a constant magnetic field on the outputsignal of each of the magnetic-field-sensitive sensors.

Preferred embodiments of the method according to the present inventionadditionally comprise the step of executing a calibration measurement soas to calculate the coefficients. In so doing, the coefficients aredetermined as matrix coefficients in such a way that a defined currentis conducted through each of the conductors in turn while the otherconductors do not carry a current. In addition, a further calibrationmeasurement is carried out in the case of which a constant magneticfield, i.e. a gradient-free magnetic field having a known magnitude, isapplied to the magnetic-field-sensitive sensors, while no current flowsthrough the conductors. For calculating the current flowing through oneor a plurality of the conductors, the sensor signals of all themagnetic-field-sensitive sensors are then linearly interconnected via amatrix operation making use of the coefficient matrix determined.

As has been mentioned hereinbefore, the magnetic-field-sensitive sensorsare preferably Hall sensors. These Hall sensors are sensitive toperpendicularly impinging magnetic fields so that the sensors arearranged between the conductors or, displaced upwards or downwards, inthe space between the conductors.

In addition, the present invention also permits the use of sensors whichare sensitive to magnetic fields impinging parallel to the surface, e.g.field plates. These sensors are arranged in such a relation to theconductors that the magnetic field generated by the conductors impingeson the sensors substantially parallel to the surface thereof.

In the following, preferred embodiments of the present invention will bedescribed in detail making reference to the drawings enclosed, in which:

FIG. 1 shows schematically a known current measuring device;

FIG. 2 shows schematically a current measuring device according to thepresent invention;

FIG. 3 shows schematically an alternative arrangement of Hall sensorsfor executing a current measurement according to the present invention;

FIG. 4 shows an arrangement of field plates for executing a currentmeasurement according to the present invention; and

FIG. 5 shows a schematic representation of the current measuring deviceaccording to the present invention.

FIG. 2 shows schematically the array of magnetic-field-sensitive sensorsaccording to the present invention used for measuring the current inthree conductors L1, L2, L3 which are arranged in close proximity to oneanother. As can be seen in FIG. 2, only four magnetic-field-sensitivesensors S1, S2, S3 and S4 are required for measuring the currents in theconductors L1, L2, L3. The four sensors are arranged in such a way thattwo respective ones of the magnetic-field-sensitive sensors, e.g. S1 andS2, are arranged adjacent a respective conductor, e.g. L1. For detectingthe current through one of the conductors, the output signals of allmagnetic-field-sensitive sensors S1 to S4 are now linearlyinterconnected via a matrix operation, the matrix coefficients beingdetermined via a calibration measurement in such a way that a definedcurrent is conducted through each of the conductors in turn while theother conductors do not carry a current.

In addition, a calibration measurement is carried out in the case ofwhich the array has applied thereto a known constant magnetic fieldwhile no current flows through the conductors.

The resultant matrix of coefficients reads:

a₁₁ a₁₂ a₁₃ a₁₄ a₂₁ a₂₂ a₂₃ a₂₄ a₃₁ a₃₂ a₃₃ a₃₄ a_(g1) a_(g2) a_(g3)a_(g4)

The coefficients a₁₁ to a₁₄ are obtained while only the conductor L1carries a known current, the coefficients a₂₁ to a₂₄ are obtained whileonly the conductor L2 carries a known current, and the coefficients a₃₁to a₃₄ are obtained while only the conductor L3 carries a known current.The coefficients a_(g1) to a_(g4) are obtained wile a known constantmagnetic field is applied and while none of the conductors carries acurrent.

The first number of the index of a respective coefficient stands for aconductor, whereas the respective second number in the index stands fora sensor so that e.g. the coefficient all describes the influence of acurrent through the conductor L1 on the output signal of the sensor S1.In the case of the coefficients a_(g1) to a_(g4) the letter g stands forthe respective constant magnetic field so that these coefficientsdescribe the influence of a constant magnetic field on the output signalof the respective sensor.

Making use of the above coefficients, the output signals A₁ to A₄ of thefour magnetic-field-sensitive sensors S1 to S4 are composed as follows:

A₁ = a₁₁ · I₁ + a₂₁ · I₂ + a₃₁ · I₃ + a_(g1) · Hg A₂ = a₁₂ · I₁ + a₂₂ ·I₂ + a₃₂ · I₃ + a_(g2) · Hg A₃ = a₁₃ · I₁ + a₂₃ · I₂ + a₃₃ · I₃ + a_(g3)· Hg A₄ = a₁₄ · I₁ + a₂₄ · I₂ + a₃₄ · I₃ + a_(g4) · Hg

wherein I₁ stands for a current through the conductor L1, I₂ stands fora current through the conductor L2, I₃ stands for a current through theconductor L3 and Hg stands for an applied constant magnetic field.

The above equations can be represented as follows in the form of amatrix or in the form of vectors:

A₁ a₁₁ a₁₂ a₁₃ a₁₄ I₁ A₂ = a₂₁ a₂₂ a₂₃ a₂₄ I₂ A₃ a₃₁ a₃₂ a₃₃ a₃₄ I₃ A₄a_(g1) a_(g2) a_(g3) a_(g4) Hg

After an inversion of the matrix of coefficients, the individualcurrents I₁ to I₃ flowing through the conductors L1 to L3 can thereforebe calculated as follows:

I₁ a₁₁ a₁₂ a₁₃ a₁₄ A₁ I₂ = a₂₁ a₂₂ a₂₃ a₂₄ · A₂ I₃ a₃₁ a₃₂ a₃₃ a₃₄ A₃ Hga_(gl) a_(g2) a_(g3) a_(g4) A₄

In this way, the current through each of the electric conductors L1 toL3 can be calculated precisely according to the present invention, onlyn−1 magnetic-field-sensitive sensors being necessary for this purpose,when the current through n conductors is to be measured. Theabove-mentioned calculating method additionally permits the detection ofthe constant magnetic field.

FIG. 3 shows a schematic representation for illustrating an alternativearray of magnetic-field-sensitive sensors with respect to threeconductors in which a current is to be measured. Also in this case, foursensors S1 to S4 are arranged with respect to three conductors L1 to L3in such a way that two respective magnetic-field-sensitive sensors arearranged adjacent a respective conductor. In this case, the sensors are,however, arranged such that they are displaced perpendicularly withrespect to an imaginary line extending through the conductors, thesensors being e.g. displaced upwards or downwards with respect to theconductors. Such an arrangement can e.g. be realized easily when thesensors are Hall sensors and when they are monolithically produced on asemiconductor substrate together with the conductors. The conductortracks L1 to L3 , which are shown in FIG. 3 only schematically with around cross-section, may here be e.g. conductor tracks on top of which adielectric layer is arranged, the magnetic-field-sensitive sensors beingthen arranged on this dielectric layer. The arrangement shown in FIG. 3,or an arrangement of the sensors directly between the conductors isused, when the sensors are sensitive to perpendicularly impingingmagnetic fields.

FIG. 4 shows an arrangement of sensors in relation to conductors incases in which the sensors are sensitive to magnetic fields impingingparallel to the surface, as in the case of field plates by way ofexample. In this arrangement the field lines of a magnetic field, whichis generated by currents through the conductors L1 to L3, extendparallel to the main surfaces of the sensors S1 to S4. Also in thiscase, only n+1 magnetic-field-sensitive sensors will be necessary formeasuring the currents through n conductors.

A schematic general representation of a current measuring deviceaccording to the present invention is shown in FIG. 5. The arrangementof the three conductors L1 to L3 and of the fourmagnetic-field-sensitive sensors S1 to S4 can be seen once more in thisrepresentation. The magnetic-field-sensitive sensors S1 to S4 are eachconnected to an evaluation unit 10. More specifically, the sensors S1 toS4 are connected to a read-out unit 12 of the evaluation unit. In theevaluation unit 10 the above-described calculation of the currentflowing through the respective conductors L1 to L3 is carried out. Inaddition, the evaluation unit 10 is preferably provided with acalibration unit 14 by means of which the above-described coefficientsare determined. For this purpose, the calibration unit 14 is connectedin a suitable manner to the respective conductors L1 to L3 so as to beable to cause a known flow of current through these conductors. This isshown in FIG. 5 by the schematically shown conductors between thecalibration unit 14 and the respective conductors L1 to L3. Furthermore,a means for generating a known constant magnetic field (not shown) ispreferably provided so as to permit the coefficients a_(g1) to a_(g4) tobe determined. Alternatively, each of these coefficients may be giventhe value 1 or some other predetermined value. In addition, theevaluation unit 10 preferably comprises a memory 16 in which thecoefficients determined are stored preferably in the form of a matrix.The coefficients can either be stored in the form determined;preferably, however, the elements of the inverted matrix are firstcalculated from the coefficients determined, these elements being thenstored in the memory 16. It is apparent that the memory 16 may beintegrated in the evaluation unit 10, although it is shown separatelyfrom this evaluation unit in FIG. 5.

It follows that the present invention provides a current measuringdevice and a method for measuring a current, respectively, in the caseof which only n+1 magnetic-field-sensitive sensors are required formeasuring the current through n conductors. Although the figures onlyshow conductors L1 to L3 which are arranged in juxtaposition, thepresent invention can also be applied to conductor arrays in which theconductors extend at right angles to one another, e.g. in a multilayeredsubstrate; also in this case, only n+1 magnetic-field-sensitive sensorsare required.

What is claimed is:
 1. A current measuring device for measuring acurrent through one or a plurality of conductors of an array of nconductors, with n being a natural number and n≧2, comprising thefollowing features: n+1 magnetic-field-sensitive sensors which arearranged in such a way that two respective magnetic-field-sensitivesensors are arranged adjacent a respective conductor; a unit for readingout output signals of the magnetic-field-sensitive sensors; and a unitfor calculating the current through one or a plurality of conductors onthe basis of the read output signals and on the basis of coefficientswhich describe the influence of currents flowing through each of the nconductors and of a constant magnetic field on the out-put signal ofeach of the magnetic-field-sensitive sensors.
 2. A current measuringdevice according to claim 1, wherein the magnetic-field-sensitivesensors (S1 to S4) are arranged such that each conductor (L1 to L3) isarranged between two of said magnetic-field-sensitive sensors.
 3. Acurrent measuring device according to claim 1, wherein a plane isdefined by the conductors in which the conductors are arranged andwherein the magnetic-field-sensitive sensors are arranged external tothe plane defined by the conductors.
 4. A current measuring deviceaccording to one of the claims 1 to 3, wherein themagnetic-field-sensitive sensors (S1 to S4) are Hall sensors.
 5. Acurrent measuring device according to claim 4, wherein the Hall sensors,together with the read-out unit (12) and the calculating unit (10), aremonolithically integrated on a semiconductor substrate.
 6. A currentmeasuring device according to one of the claims 1 to 5, wherein thecoefficients in the form of a matrix are stored in a memory means (16).7. A current measuring device according to claim 6 referring back toclaim 5, wherein the memory means (16) is integrated on thesemiconductor substrate.
 8. A method of measuring the current throughone or a plurality of conductors of an array of n conductors, with nbeing a natural number and n≧2, comprising the following steps: readingout the output signals of n+1 magnetic-field-sensitive sensors, tworespective ones of said sensors being arranged adjacent a respectiveconductor; calculating the current through one or a plurality of theconductors an the basis of the read output signals and on the basis ofcoefficients which describe the influence of currents flowing througheach of the n conductors and of a constant magnetic field on the outputsignal of each of the magnetic-field-sensitive sensors.
 9. A methodaccording to claim 8, comprising in addition the step of determining thecoefficients on the basis of the output signal of each of themagnetic-field-sensitive sensors (S1 to S4) while a known flow ofcurrent is successively caused through each of the conductors, whereasno current flows through the rest of the conductors, and on the basis ofthe output signal of each of the magnetic-field-sensitive sensors (S1 toS4) during application of a known constant magnetic field, while nocurrent flows through the conductors.
 10. A method according to claim 9,comprising in addition the step of storing the coefficients.
 11. Amethod according to claim 8, wherein the calculation step comprises theexecution of a linear interconnection of the output signals of themagnetic-field-sensitive sensors by means of a matrix operation, thecoefficients which describe the influence of currents flowing througheach of the n conductors and of a constant magnetic field on the outputsignal of each of the magnetic field-sensitive sensors being used asmatrix coefficients.